The Role Of Mitochondria In Embryo Development

Mitochondria play a key role in the physiology of eukaryotic cells. They are important for mammalian oocyte and preimplantation embryo development, as well as for nuclear transplantation and stem cells (Bavister and Squirrell, 2000; Cummins, 2001a, 2002; Hiendleder and Wolf, 2003). This is not only due to the fundamental role of mitochondria in energy metabolism, but also because they are semi-autonomous organelles and each one contains one or several copies of its genome (mtDNA) that must be replicated during embryo development. In humans, the mitochondrial genome is a 16.6kb circular strand of DNA encoding 37 genes. These include 13 components of the oxidative phosphorylation (OXPHOS) pathway, two ribosomal RNAs and 22 transfer RNAs. The coding capacity of mtDNA is quite limited, because over 200 of the genes needed for mitochondrial function actually reside in the cell's nuclear genome (Cummins, 2001a). This indicates that most of the original mitochondrial genome has migrated to the cell nucleus, with only a small subset of genes remaining within the mitochondrion for OXPHOS control. Existence of this arrangement is verified by several mutations found either in the nuclear and/or mitochondrial genes that impair OXPHOS; potentially lethal disorders are often associated with these mutations (Thorburn and Dahl, 2001). As a result, we know that mitochondrial functions depend on cytoplasm-nucleus information exchange. This exchange is exerted through nuclear-encoded transcription factors, such as mitochondrial transcription factor A (TFAM), that regulate mitochondrial biogenesis and energy metabolic functions.

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